Shpkpr 1 gives 200rs good to lady..lets call it as loss1…. shkpr1 gives 800 rs change to lady..lets call it as loss2…. now when shpkpr2 says that note is duplicate…shpkpr 1 has to returnn his 1000rs….. but he has only 200 in hand…. so he has to put 800 more…lets call that as loss3… so loss1+loss2+loss3 = 1800